Update docs

Description

This includes undocumented but required steps for installing natlink. This'll save me (and the next person) 30-60 minutes of effort the next time they install caster.

I also renamed the bullet points in the section to 1.. This makes it easy to rearrange, add, and delete bullet points without needing to re-number them all, but it renders in the correct order.

Related Issue

Motivation and Context

How Has This Been Tested

Types of changes

[x] Docs change / refactoring / dependency upgrade
[ ] Bug fix (non-breaking change which fixes an issue or bug)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)
[ ] Renamed existing command phrases (we discourage this without a strong rationale).

Checklist

[x] I have read the CONTRIBUTING document.
[ ] My code follows the code style of this project.
[x] I have checked that my code does not duplicate functionality elsewhere in Caster.
[x] My code implements all the features I wish to merge in this pull request.
[x] My change requires a change to the documentation.
[x] I have updated the documentation accordingly.
[ ] I have added tests to cover my changes.
[ ] All new and existing tests pass.

Maintainer/Reviewer Checklist

[ ] Basic functionality has been tested and works as claimed.
[ ] New documentation is clear and complete.
[ ] Code is clear and readable.

dictation-toolbox / Caster

Included additional steps for installing natlink #936